Radio station, transmitting station, and frequency band sharing method

ABSTRACT

The invention has a step where a transmitting station in a second radio communication system determines whether transmission of a second radio communication system signal using a shared frequency band is possible or not based on load information of a first radio communication system broadcast from a base station in the first radio communication system, a step where the transmitting station in the second radio communication system calculates predicted interference power caused in a receiving station in the first radio communication system by the second radio communication system signal transmitted using the shared frequency band, and a step where the base station in the first radio communication system increases an allowable interference level of a first radio communication system signal transmitted using the shared frequency band based on the predicted interference power broadcast from the transmitting station in the second radio communication system.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2009-164244, filed on Jul. 10,2009; the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a radio station in a first radiocommunication system using a shared frequency band which the first radiocommunication system uses in priority to a second radio communicationsystem, a transmitting station in the second radio communication system,and a method of sharing the frequency band.

BACKGROUND

Conventionally, as a technique of sharing frequencies among a pluralityof radio communication systems including a priority system and anon-priority system, such a technique is known that the non-prioritysystem transmits a signal using a shared frequency band in accordancewith the presence or absence of a signal of the priority system in theshared frequency band (for example, Japanese Unexamined PatentPublication No. 2006-222665).

More specifically, the non-priority system determines whether there is asignal from the priority system in the shared frequency band beforetransmitting a signal from the non-priority system. To prevent aninterference in the priority system from causing by a transmissionsignal from the non-priority system, the non-priority system transmits asignal using the shared frequency band only when a signal from thepriority system is not present.

However, in the above-mentioned conventional technique, even when theload of the priority system is allowable, the non-priority system doesnot transmit a signal in the case where a signal from the prioritysystem exits. Therefore, a problem arises that although the load of thepriority system is allowable, a transmission opportunity of a signalfrom the non-priority system is restricted.

Further, to increase the transmission opportunity from the non-prioritysystem in the above-mentioned conventional technique, it is consideredthat the non-priority system transmits a signal even when a signal fromthe priority system exists. However, in this case, when a receiver inthe priority system is located near a transmitter in the non-prioritysystem, an interference level in the receiver in the priority systemrapidly increases by a transmission signal from the non-priority system.Therefore, there is a problem that signal quality deteriorates in thepriority system.

SUMMARY OF THE INVENTION

The present invention was made in view of such a respect, and it is anobject of the invention to provide a radio station, a transmittingstation and a frequency band sharing method for increasing transmissionopportunities of signals in a non-priority system, while preventingsignal quality from deteriorating in a priority system, when frequenciesare shared among a plurality of radio communication systems includingthe priority system and non-priority system.

A radio station of the invention is a radio station for controlling afirst radio communication system signal (uplink signal UL1 or downlinksignal DL1) transmitted using a shared frequency band which the firstradio communication system uses in priority to a second radiocommunication system, and is characterized by having a broadcast section(broadcast signal transmitting/receiving section 103) that broadcastsload information of the first radio communication system to atransmitting station in the second radio communication system, anacquisition section (broadcast signal transmitting/receiving section103) that acquires predicted interference power caused in a receivingstation in the first radio communication system by a second radiocommunication system signal that is transmitted using the sharedfrequency band from the transmitting station in the second radiocommunication system, and an allowable interference level controlsection (allowable interference level control section 104) thatincreases an allowable interference level of the first radiocommunication system signal transmitted using the shared frequency band,based on the predicted interference power acquired in the acquisitionsection.

According to this configuration, the broadcast section broadcasts theload information of the first radio communication system to thetransmitting station in the second radio communication system, and it isthereby possible to increase the transmission opportunity of the secondradio communication system signal transmitted from the transmittingstation in the second radio communication system. Further, by increasingthe allowable interference level of the first radio communication systemsignal based on the predicted interference power acquired in theacquisition section, it is possible to prevent the quality of the firstradio communication system signal received in the receiving station inthe first radio communication system from deteriorating due to thesecond radio communication system signal transmitted using the sharedfrequency band.

Further, in the radio station, the allowable interference level controlsection increases transmission power of the first radio communicationsystem signal or decreases a transmission rate of the first radiocommunication system signal based on the predicted interference poweracquired in the acquisition section.

Furthermore, it may be preferable that the radio station further has afrequency band switching section (resource allocation control section106) that switches the frequency band of the first radio communicationsystem signal from the shared frequency band to a dedicated frequencyband of the first radio communication system, the acquisition sectionacquires priority information of the first radio communication systemsignal and the second radio communication system signal, and receptionquality information of the first radio communication system signal inaddition to the predicted interference power, and that the frequencyband switching section switches the frequency band of the first radiocommunication system signal from the shared frequency band to thededicated frequency band based on at least one of the priorityinformation and the reception quality information.

Still furthermore, it may be preferable that in the radio station, theacquisition section acquires load information of the second radiocommunication system in addition to the predicted interference power,the priority information and the reception quality information, and thatthe frequency band switching section switches the frequency band of thefirst radio communication system signal from the shared frequency bandto the dedicated frequency band based on at least one of the priorityinformation, the reception quality information, and the load informationof the second radio communication system.

Moreover, the radio station further can have an adjacent cellinterference control section (adjacent cell interference control section107) that decreases interference power caused in the receiving stationin the first radio communication system by an adjacent cell based on thepredicted interference power acquired in the acquisition section.

A transmitting station of the invention is a transmitting station (basestation BS2 or mobile station MT2) for transmitting a second radiocommunication system signal (downlink signal DL2 or uplink signal UL2)to a receiving station in the second radio communication system using ashared frequency band which a first radio communication system uses inpriority to the second radio communication system, and is characterizedby having an acquisition section (broadcast signaltransmitting/receiving section 201) that acquires load information ofthe first radio communication system, a transmission determining section(transmission determining section 202) that determines whethertransmission of the second radio communication system signal using theshared frequency band is possible or not based on the load informationacquired in the acquisition section, a predicted interference powercalculating section (predicted interference power calculating section204) that calculates predicted interference power caused in a receivingstation (base station BS1 or mobile station MT1) in the first radiocommunication system by the second radio communication system signaltransmitted using the shared frequency band, and a broadcast section(broadcast signal transmitting/receiving section 201) that broadcaststhe predicted interference power calculated in the predictedinterference power calculating section to the first radio communicationsystem.

According to this configuration, by determining whether transmission ofthe second radio communication system signal using the shared frequencyband is possible or not based on the load information of the first radiocommunication system acquired in the acquisition section, it is possibleto increase the transmission opportunity of the second radiocommunication system signal transmitted from the transmitting station inthe second radio communication system. Further, the broadcast sectionbroadcasts the predicted interference power to the receiving station ortransmitting station in the first radio communication system, and it isthereby possible to prevent the quality of the first radio communicationsystem signal received in the receiving station in the first radiocommunication system from deteriorating due to the second radiocommunication system signal transmitted using the shared frequency band.

Further, the station can have a channel state estimating section(channel state estimating section 206) that estimates a channel statebetween the receiving station in the first radio communication systemand the transmitting station, and that the transmission possibilitydetermining section determines whether transmission of the second radiocommunication system signal using the shared frequency band is possibleor not based on the load information acquired in the acquisition sectionand the channel state estimated in the channel state estimating section.

Furthermore, in the transmitting station, the broadcast sectionbroadcasts priority information of the second radio communication systemsignal transmitted using the shared frequency band in addition to thepredicted interference power.

Still furthermore, in the transmitting station, the broadcast sectionbroadcasts load information of the second radio communication system inaddition to the predicted interference power and the priorityinformation.

A frequency band sharing method of the invention is a frequency bandsharing method in which a first radio communication system and a secondradio communication system share a shared frequency band which the firstradio communication system uses in priority to the second radiocommunication system, and is characterized by having a step where aradio station in the first radio communication system broadcasts loadinformation of the first radio communication system to a transmittingstation in the second radio communication system, a step where thetransmitting station in the second radio communication system determineswhether transmission of a second radio communication system signal fromthe transmitting station using the shared frequency band is possible ornot based on the broadcast load information of the first radiocommunication system, a step where the transmitting station in thesecond radio communication system calculates predicted interferencepower caused in a receiving station in the first radio communicationsystem by the second radio communication system signal transmitted usingthe shared frequency band, a step where the transmitting station in thesecond radio communication system broadcasts the calculated predictedinterference power to the radio station in the first radio communicationsystem, and a step where the radio station in the first radiocommunication system increases an allowable interference level of afirst radio communication system signal transmitted using the sharedfrequency band based on the broadcast predicted interference power.

It is possible to provide a radio station, transmitting station andfrequency band sharing method for increasing transmission opportunitiesof signals in a non-priority system, while preventing signal qualityfrom deteriorating in a priority system, when frequencies are sharedamong a plurality of radio communication systems including the prioritysystem and non-priority system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a radio communication system accordingto Embodiment 1 of the invention;

FIG. 2 is a configuration diagram of a base station according toEmbodiment 1 of the invention;

FIG. 3 is a diagram to explain allowable interference level controlaccording to Embodiment 1 of the invention;

FIG. 4 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 1 of the invention;

FIG. 5 is a diagram to explain a communication environment according toEmbodiment 1 of the invention;

FIG. 6 is a diagram to explain a communication environment according toModification 1-1 of the invention;

FIG. 7 is a diagram to explain a communication environment according toModification 1-2 of the invention;

FIG. 8 is a diagram to explain a communication environment according toModification 1-3 of the invention;

FIG. 9 is a configuration diagram of a base station according toEmbodiment 2 of the invention;

FIG. 10 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 2 of the invention;

FIG. 11 is a configuration diagram of a base station according toEmbodiment 3 of the invention;

FIG. 12 is a diagram to explain resource allocation control according toEmbodiment 3 of the invention;

FIG. 13 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 3 of the invention;

FIG. 14 is a configuration diagram of a base station or mobile stationaccording to Embodiment 4 of the invention;

FIG. 15 is a configuration diagram of a base station according toEmbodiment 5 of the invention;

FIG. 16 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 5 of the invention;

FIG. 17 is a configuration diagram of a base station according toEmbodiment 6 of the invention;

FIG. 18 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 6 of the invention; and

FIG. 19 is a flowchart illustrating frequency band sharing processingaccording to Embodiment 7 of the invention.

DETAILED DESCRIPTION

Embodiments of the invention will specifically be described below withreference to accompanying drawings.

Embodiment 1

FIG. 1 is a schematic diagram of a radio communication system accordingto Embodiment 1 of the invention. As shown in FIG. 1, a radiocommunication system 1 and radio communication system 2 are operated inthe same or adjacent areas.

Further, the radio communication system 1 and radio communication system2 share the same or adjacent frequency bands. In use of the sharedfrequency band, the radio communication system 1 has a priority over theradio communication system 2. In other words, the radio communicationsystem 1 is a priority system, and the radio communication system 2 is anon-priority system.

The radio communication system 1 is comprised of a base station BS1 andmobile stations MT11 and MT12. The base station BS1 receives uplinksignals UL1 from the mobile stations MT11 and MT12 existing in a cellC1, while transmitting downlink signals DL1 to the mobile stations MT11and MT12. The radio communication system 1 is a mobile communicationsystem, for example. In addition, the mobile stations MT11 and MT12 inthe radio communication system 1 have the same configuration, andtherefore, are referred to as a mobile station MT1 except when they aredistinguished. Further, a first radio communication system signal is ageneric term for the downlink signal DL1 and uplink signal UL1.Furthermore, a radio station in the radio communication system 1 is ageneric term for the base station BS1 and mobile station MT1.

The radio communication system 2 is comprised of a base station BS2 andmobile stations MT21 and MT22. The base station BS2 receives uplinksignals UL2 from the mobile stations MT21 and MT22 existing in a cellC2, while transmitting downlink signals DL2 to the mobile stations MT21and MT22. The radio communication system 2 is a mobile communicationsystem or wireless LAN system, for example. In addition, the mobilestations MT21 and MT22 have the same configuration, and therefore, arereferred to as a mobile station MT2 except when they are distinguished.Further, a second radio communication system signal is a generic termfor the downlink signal DL2 and uplink signal UL2. Furthermore, a radiostation in the radio communication system 2 is a generic term for thebase station BS2 and mobile station MT2.

As described above, the radio communication system 1 and radiocommunication system 2 share the shared frequency band which the radiocommunication system 1 preferentially uses. Herein, it is assumed thatthe radio communication system 1 uses the shared frequency band ineither the uplink signal UL1 or downlink signal DL1. Similarly, it isassumed that the radio communication system 2 uses the shared frequencyband in either the uplink signal UL2 or downlink signal DL2.

In the following, Embodiment 1 describes the case where the sharedfrequency band is shared between the uplink signal UL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2. In this case, a receiving station in the radiocommunication system 1 is the base station BS1 that receives the uplinksignal UL1, and a transmitting station in the radio communication system2 is the base station BS2 that transmits the downlink signal DL2.

FIG. 2 is a configuration diagram of the base station BS1 in the radiocommunication system 1 and the base station BS2 in the radiocommunication system 2. As shown in FIG. 2, the base station BS1 in theradio communication system 1 is provided with a signaltransmitting/receiving section 101, load information collecting section102, broadcast signal transmitting/receiving section 103, and allowableinterference level control section 104.

The signal transmitting/receiving section 101 receives the uplink signalUL1 from the mobile station MT1. Further, the signaltransmitting/receiving section 101 transmits the downlink signal DL1 tothe mobile station, while transmitting an allowable interference controlsignal based on instructions from the allowable interference levelcontrol section 104 described later.

The load information collecting section 102 collects load information inthe radio communication system 1. Herein, the load information includesa traffic amount of the cell of the BS1, traffic amounts of adjacentcells, reception quality information, etc. In Embodiment 1, since theshared frequency band is used in the uplink signal UL1, as the loadinformation, the load information collecting section 102 collects thetraffic amount of the uplink signal UL1, reception quality informationof the uplink signal UL1, etc.

The broadcast signal transmitting/receiving section 103 (broadcastsection, acquisition section) transmits and receives a broadcast signalto/from the base station BS2 in the radio communication system 2. Thebroadcast signal transmitted to the base station BS2 includes the loadinformation collected in the load information collecting section 102.Further, the broadcast signal received from the base station BS2includes predicted interference power caused in the base station BS1 bythe downlink signal DL2 to be transmitted from the base station BS2using the shared frequency band.

In addition, the broadcast signal transmitting/receiving section 103 maytransmit and receive the broadcast signal via a backbone networkconnecting between the radio communication system 1 and the radiocommunication system 2, or may transmit and receive the broadcast signalvia direct wireless communication between the base station BS1 and thebase station BS2.

The allowable interference level control section 104 increases theallowable interference level of the uplink signal UL1 transmitted usingthe shared frequency band, based on the predicted interference powerfrom the base station BS2. More specifically, the allowable interferencelevel control section 104 instructs the mobile station MT1 to increasethe transmission power of the uplink signal UL1 or decrease atransmission rate of the uplink signal UL1, based on the predictedinterference power from the base station BS2.

As shown in FIG. 3, when the allowable interference level is increased,even in the case where the interference signal level is increased by anallowable interference level margin due to the predicted interferencepower from the base station BS2, it is possible to maintain the signalto interference ratio (SIR) of the uplink signal UL1 at a certain level.

The base station BS2 (transmitting station) in the radio communicationsystem 2 is provided with a broadcast signal transmitting/receivingsection 201, transmission possibility determining section 202,transmission parameter determining section 203, predicted interferencepower calculating section 204, and signal transmitting/receiving section205.

The broadcast signal transmitting/receiving section 201 (acquisitionsection, broadcast section) receives a broadcast signal including theload information from the base station BS1 in the radio communicationsystem 1. Further, the broadcast signal transmitting/receiving section201 transmits a broadcast signal including the predicted interferencepower calculated in the predicted interference power calculating section204, described later, to the base station BS1 in the radio communicationsystem 1.

The transmission possibility determining section 202 determines whethertransmission of the downlink signal DL2 using the shared frequency bandis possible or not based on the load information from the base stationBS1. More specifically, the transmission possibility determining section202 estimates an allowable interference level margin of the radiocommunication system 1 based on the load information, and determineswhether or not the estimated allowable interference level margin is apredetermined value or more. The transmission possibility determiningsection 202 determines that it is possible to transmit the downlinksignal DL2 when the allowable interference level margin of the radiocommunication system 1 is the predetermined value or more. Thetransmission possibility determining section 202 determines that it isnot possible to transmit the downlink signal DL2 when the allowableinterference level margin of the radio communication system 1 is lessthan the predetermined value.

The transmission parameter determining section 203 determinestransmission parameters of the downlink signal DL2 from the base stationBS2. More specifically, the transmission parameter determining section203 determines the transmission power, modulation scheme, coding rate,etc. of the downlink signal DL2.

The predicted interference power calculating section 204 calculates thepredicted interference power caused in the base station BS1 in the radiocommunication system 1 by the downlink signal DL2 to be transmittedusing the shared frequency band, based on the transmission power of thedownlink signal DL2 determined in the transmission parameter determiningsection 203.

The signal transmitting/receiving section 205 transmits the downlinksignal DL2 to the mobile station MT2 according to the transmissionparameters determined in the transmission parameter determining section203. Further, the signal transmitting/receiving section 205 receives theuplink signal UL2 from the mobile station MT2.

The frequency band sharing processing according to Embodiment 1 will bedescribed below with reference to FIGS. 4 and 5. In Embodiment 1, asdescribed above, the shared frequency band is shared between the uplinksignal UL1 in the radio communication system 1 and the downlink signalDL2 in the radio communication system 2, and the frequency band sharingprocessing is performed between the base station BS1 (receiving station)in the radio communication system 1 and the base station BS2(transmitting station) in the radio communication system 2.

As shown in FIG. 4, the load information collecting section 102 in thebase station BS1 collects the load information of the uplink signal UL1(step S101).

The broadcast signal transmitting/receiving section 103 in the basestation BS1 transmits a broadcast signal including the collected loadinformation of the uplink signal UL1 to the base station BS2 (stepS102). The broadcast signal transmitting/receiving section 201 in thebase station BS2 receives the broadcast signal including the loadinformation of the uplink signal UL1 from the base station BS1 (stepS103).

The transmission determining section 202 in the base station BS2determines whether transmission of the downlink signal DL2 is possibleor not based on the load information of the uplink signal UL1 broadcastfrom the base station BS1 (step S104). More specifically, when theallowable interference level margin estimated based on the loadinformation of the uplink signal UL1 is a predetermined value or more,the transmission determining section 202 determines that it is possibleto transmit the downlink signal DL2. Meanwhile, when the allowableinterference level margin is less than the predetermined value, thetransmission determining section 202 determines that it is not possibleto transmit the downlink signal DL2, and waits for transmission of thedownlink signal DL2 (step S105).

When it is determined that the downlink signal DL2 can be transmitted,the transmission parameter calculating section 203 of the base stationBS2 determines the transmission power of the downlink signal DL2. Thepredicted interference power calculating section 204 in the base stationBS2 calculates the predicted interference power caused in the basestation BS1 by the downlink signal DL2 to be transmitted using theshared frequency band, based on the determined transmission power of thedownlink signal DL2 (step S106).

The broadcast signal transmitting/receiving section 201 in the basestation BS2 transmits a broadcast signal including the predictedinterference power calculated in step S106 to the base station BS1 (stepS107). The broadcast signal transmitting/receiving section 103 in thebase station BS1 receives the broadcast signal including the predictedinterference power calculated in step S106 (step S108).

The allowable interference level control section 104 in the base stationBS1 instructs the mobile station MT1 to increase the transmission powerof the uplink signal UL1 or decrease a transmission rate of the signalUL1 based on the predicted interference power broadcast from the basestation BS2 (step S109).

The signal transmitting/receiving section 205 in the base station BS2transmits the downlink signal DL2 to the mobile station MT2 with thetransmission power determined in step S106 (step S110).

According to the base station BS1 in the radio communication system 1and the base station BS2 in the radio communication system 2 accordingto Embodiment 1, when a shared frequency band is shared between theuplink signal UL1 in the radio communication system 1 and the downlinksignal DL2 in the radio communication system 2, it is determined whetheror not transmission of the downlink signal DL2 from the base station BS2is possible based on the load information of the uplink signal UL1collected in the base station BS1, and it is thereby possible toincrease the transmission opportunity of the downlink signal DL2 fromthe base station BS2.

Further, the base station BS1 increases the allowable interference levelof the uplink signal UL1 based on the predicted interference powerbroadcast from the base station BS2, and it is thereby possible toprevent the quality of the uplink signal UL1 received in the basestation BS1 from deteriorating due to interference from the downlinksignal DL2 transmitted from the base station BS2.

(Modification 1-1)

Modification 1-1 in Embodiment 1 describes the case where a sharedfrequency band is shared between the uplink signal UL1 in the radiocommunication system 1 and the uplink signal UL2 in the radiocommunication system 2.

Referring to FIG. 6, the frequency band sharing processing according toModification 1-1 will be described, while focusing on the differencefrom the frequency band sharing processing in above-mentionedEmbodiment 1. In Modification 1-1, the mobile station MT2 is providedwith the configuration of the base station BS2 as shown in FIG. 2, andthe above-mentioned frequency band sharing processing is performedbetween the base station BS1 (receiving station) in the radiocommunication system 1 and the mobile station MT2 (transmitting station)in the radio communication system 2.

More specifically, as shown in FIG. 6, the mobile station MT2 in theradio communication system 2 receives a broadcast signal transmittedfrom the base station BS1 in the radio communication system 1 via thebase station BS2. The mobile station MT2 determines whether or nottransmission of the uplink signal UL2 is possible based on the loadinformation of the uplink signal UL1 included in the broadcast signal.The mobile station MT2 determines the transmission power of the uplinksignal UL2 when determining that it is possible to the signal UL2. Themobile station MT2 calculates the predicted interference power caused inthe base station BS1 by the uplink signal UL2 to be transmitted usingthe shared frequency band, based on the determined transmission power ofthe uplink signal UL2. The mobile station MT2 transmits a broadcastsignal including the calculated predicted interference power to the basestation BS1 in the radio communication system 1.

The base station BS1 in the radio communication system 1 transmits anallowable interference level control signal to the mobile station MT1.The base station BS1 instructs the mobile station MT1 to increase thetransmission power of the uplink signal UL1 or decrease a transmissionrate of the uplink signal UL1 based on the predicted interference powerbroadcast from the mobile station MT2, using the allowable interferencelevel control signal.

According to the base station BS1 in the radio communication system 1and the mobile station MT2 in the radio communication system 2 accordingto Modification 1-1, when a shared frequency band is shared between theuplink signal UL1 in the radio communication system 1 and the uplinksignal UL2 in the radio communication system 2, it is determined whethertransmission of the uplink signal DL2 from the mobile station MT2 ispossible or not based on the load information of the uplink signal UL1collected in the base station BS1, and it is thereby possible toincrease the transmission opportunity of the uplink signal UL2 from themobile station MT2.

Further, the base station BS1 increases the allowable interference levelof the uplink signal UL1 based on the predicted interference powerbroadcast from the mobile station MT2, and it is thereby possible toprevent the quality of the uplink signal UL1 received in the basestation BS1 from deteriorating due to interference from the uplinksignal UL2 transmitted by the mobile station MT2.

(Modification 1-2)

Modification 1-2 in Embodiment 1 describes the case where a sharedfrequency band is shared between the downlink signal DL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2.

Referring to FIG. 7, the frequency band sharing processing according toModification 1-2 will be described, while focusing on the differencefrom the frequency band sharing processing in above-mentionedEmbodiment 1. In Modification 1-2, the above-mentioned frequency bandsharing processing is performed between the base station BS1(transmitting station) in the radio communication system 1 and the basestation BS2 (transmitting station) in the radio communication system 2.

More specifically, as shown in FIG. 7, the base station BS1 in the radiocommunication system 1 collects reception quality information of thedownlink signal DL1 from each mobile station MT1. The base station BS1transmits to the base station BS2 a broadcast signal including all ofthe collected reception quality information or an average value of thecollected reception quality information as the load information of thedownlink signal DL1.

The base station BS2 receiving the broadcast signal calculates thepredicted interference power caused in the mobile station MT1 by thedownlink signal DL2 to be transmitted using the shared frequency band,and transmits a broadcast signal including the calculated predictedinterference power to the base station BS1.

The base station BS1 performs allowable interference level control forincreasing the transmission power of the downlink signal DL1 to themobile station MT1 or decreasing the transmission rate of the signalDL1, based on the predicted interference power broadcast from the basestation BS2.

According to the base station BS1 in the radio communication system 1and the base station BS2 in the radio communication system 2 accordingto Modification 1-2, when a frequency band is shared between thedownlink signal DL1 in the radio communication system 1 and the downlinksignal DL2 in the radio communication system 2, it is determined whethertransmission of the downlink signal DL2 from the base station BS2 ispossible or not based on the load information of the downlink signal DL1collected in the base station BS1, and it is thereby possible toincrease the transmission opportunity of the downlink signal DL2 fromthe base station BS2.

Further, the base station BS1 increases the allowable interference levelof the downlink signal DL1 based on the predicted interference powerbroadcast from the base station BS2, and it is thereby possible toprevent the quality of the downlink signal DL1 received in the mobilestation MT1 from deteriorating due to interference from the downlinksignal DL2 transmitted by the base station BS2.

(Modification 1-3)

Modification 1-3 in Embodiment 1 describes the case where a frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 in the radiocommunication system 2.

Referring to FIG. 8, the frequency band sharing processing according toModification 1-3 will be described, while focusing on the differencefrom Modification 1-1 and Modification 1-2. In Modification 1-3, themobile station MT2 is provided with the configuration of the basestation BS2 as shown in FIG. 2, and the above-mentioned frequency bandsharing processing is performed between the base station BS1(transmitting station) in the radio communication system 1 and themobile station MT2 (transmitting station) in the radio communicationsystem 2.

As shown in FIG. 8, the mobile station MT2 in the radio communicationsystem 2 calculates the predicted interference power caused in themobile station MT1 by the uplink signal UL2 to be transmitted from themobile station MT2 using the shared frequency band, as described inModification 1-1. The mobile station MT2 broadcasts the calculatedpredicted interference power to the base station BS1.

The base station BS1 in the radio communication system 1 increases thetransmission power of the downlink signal DL1 to the mobile station MT1or decreases the transmission rate of the downlink signal DL1 based onthe predicted interference power broadcast from the base station BS2, asdescribed in Modification 1-2.

According to the base station BS1 in the radio communication system 1and the mobile station MT2 in the radio communication system 2 accordingto Modification 1-3, when a frequency band is shared between thedownlink signal DL1 in the radio communication system 1 and the uplinksignal UL2 in the radio communication system 2, it is determined whethertransmission of the uplink signal UL2 from the mobile station MT2 ispossible or not based on the load information of the downlink signal DL1collected in the base station BS1, and it is thereby possible toincrease the transmission opportunity of the uplink signal UL2 from themobile station MT2.

Further, the base station BS1 increases the allowable interference levelof the downlink signal DL1 based on the predicted interference powerbroadcast from the mobile station MT2, and it is thereby possible toprevent the quality of the downlink signal DL1 received in the mobilestation MT1 from deteriorating due to interference from the uplinksignal UL2 transmitted by the mobile station MT2.

Embodiment 2

Referring to FIG. 9, the base station BS2 in the radio communicationsystem 2 according to Embodiment 2 of the invention will be describedbelow, while focusing on the difference from that in Embodiment 1.

In the following, Embodiment 2 describes the case where a sharedfrequency band is shared between the uplink signal UL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2 (see FIG. 5).

As shown in FIG. 9, the base station BS2 in the radio communicationsystem 2 has a channel state estimating section 206, and in thisrespect, differs from that in Embodiment 1.

The channel state estimating section 206 in the base station BS2estimates a channel state between the base station BS1 (receivingstation) in the radio communication system 1 and the base station BS2(transmitting station) in the radio communication system 2. For example,the channel state estimating section 206 estimates the channel statebetween the base station BS1 and base station BS2 based on the receptionstrength of a broadcast signal transmitted from the base station BS1.Further, the channel state estimating section 206 may estimate theaforementioned channel state based on the reception strength of a knownsymbol from the base station BS1.

The frequency band sharing processing according to Embodiment 2 will bedescribed below with reference to FIG. 10. In Embodiment 2, thefrequency band sharing processing is performed between the base stationBS1 (receiving station) in the radio communication system 1 and the basestation BS2 (transmitting station) in the radio communication system 2.In addition, steps S201 to S203 are the same as steps S101 to S103 inFIG. 4, and descriptions thereof are omitted.

As described above, the channel state estimating section 206 in the basestation BS2 estimates the channel state between the base station BS1 andbase station BS2 (step S204).

The transmission determining section 202 in the base station BS2determines whether transmission of the downlink signal DL2 is possibleor not based on the load information broadcast from the base station BS1and the estimated channel state between the base station BS1 and basestation BS2 (step S205). More specifically, the transmission determiningsection 202 determines whether or not the mobile station MT1 thattransmits the uplink signal UL1 exists near the base station BS2, basedon the channel state between the base station BS1 and base station BS2.

For example, even when the allowable interference level margin of theradio communication system 1 that is estimated based on the loadinformation is a predetermined value or more, in the case where thetransmission determining section 202 determines that the mobile stationMT1 that transmits the uplink signal UL1 exists near the base stationBS2, the section 202 determines that it is not possible to transmit thedownlink signal DL2, and waits for transmission of the downlink signalDL2 (step S206).

When determining that it is possible to transmit the downlink signalDL2, the transmission parameter determining section 203 in the basestation BS2 determines the transmission power of the downlink signal DL2based on the estimated channel state. The predicted interference powercalculating section 204 calculates the predicted interference powercaused in the base station BS1 by the downlink signal DL2 to betransmitted using the shared frequency band, based on the transmissionpower of the downlink signal DL2 determined in the transmissionparameter determining section 203 (step S207). Steps S208 to S211 arethe same as steps S107 to S110 in FIG. 4, and descriptions thereof areomitted.

According to the base station BS2 in the radio communication system 2according to Embodiment 2, when a shared frequency band is sharedbetween the uplink signal UL1 in the radio communication system 1 andthe downlink signal DL2 in the radio communication system 2, it isdetermined whether transmission of the downlink signal DL2 from the basestation BS2 is possible or not based on the channel state between thebase station BS1 and base station BS2, in addition to the loadinformation collected in the base station BS1. Therefore, when themobile station MT1 that transmits the uplink signal UL1 exists near thebase station BS2, it is possible to prevent the quality of the uplinksignal UL1 transmitted from the mobile station MT1 from deterioratingdue to interference from the downlink signal DL2 transmitted from thebase station BS2.

(Modification 2-1)

Modification 2-1 in Embodiment 2 describes the case where a frequencyband is shared between the uplink signal UL1 in the radio communicationsystem 1 and the uplink signal UL2 in the radio communication system 2(see FIG. 6), while focusing on the difference from Embodiment 2.

In the frequency band sharing processing according to Modification 2-1,the mobile station MT2 (transmitting station) is provided with theconfiguration of the base station BS2 as shown in FIG. 9. The channelstate estimating section 206 in the mobile station MT2 estimates achannel state between the base station BS1 (receiving station) in theradio communication system 1 and the mobile station MT2 (transmittingstation) in the radio communication system 2. For example, the channelstate estimating section 206 estimates the above-mentioned channel statebased on the reception strength of a known symbol from the base stationBS1.

The transmission determining section 202 in the mobile station MT2determines whether transmission of the uplink signal UL2 from the mobilestation MT2 is possible or not based on the load information from thebase station BS1 and the estimated channel state.

According to the mobile station MT2 in the radio communication system 2according to Modification 2-1, when a frequency band is shared betweenthe uplink signal UL1 in the radio communication system 1 and the uplinksignal UL2 in the radio communication system 2, it is determined whethertransmission of the uplink signal UL2 from the mobile station MT2 ispossible or not based on the channel state between the base station BS1and mobile station MT2, in addition to the load information collected inthe base station BS1. Therefore, when the mobile station MT1 thattransmits the uplink signal UL1 exists near the mobile station MT2, itis possible to prevent the quality of the uplink signal UL1 transmittedfrom the mobile station MT1 from deteriorating due to interference fromthe uplink signal UL2 transmitted from the mobile station MT2.

(Modification 2-2)

Modification 2-2 in Embodiment 2 describes the case where a frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2 (see FIG. 7), while focusing on the differencefrom Embodiment 2.

In the frequency band sharing processing according to Modification 2-2,the channel state estimating section 206 in the base station BS2estimates a channel state between the mobile station MT1 (receivingstation) in the radio communication system 1 and the base station BS2(transmitting station) in the radio communication system 2. For example,the channel state estimating section 206 in the base station BS2estimates the channel state based on a known symbol of an uplinktransmission signal from the mobile station MT1. The transmissiondetermining section 202 in the base station BS2 determines whethertransmission of the downlink signal DL2 from the base station BS2 ispossible or not based on the load information broadcast from the basestation BS1 and the estimated channel state.

According to the base station BS2 in the radio communication system 2according to Modification 2-2, when a frequency band is shared betweenthe downlink signal DL1 in the radio communication system 1 and thedownlink signal DL2 in the radio communication system 2, it isdetermined whether transmission of the downlink signal DL2 from the basestation BS2 is possible or not based on the channel state between themobile station MT1 and base station BS2, in addition to the loadinformation collected in the base station BS1. Therefore, when the basestation BS1 that transmits the downlink signal DL1 exists near the basestation BS2, it is possible to prevent the quality of the downlinksignal DL1 transmitted from the base station BS1 from deteriorating dueto interference from the downlink signal DL2 transmitted from the basestation BS2.

(Modification 2-3)

Modification 2-3 in Embodiment 2 describes the case where a frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 in the radiocommunication system 2 (see FIG. 8), while focusing on the differencefrom Embodiment 2.

In the frequency band sharing processing according to Modification 2-3,the mobile station MT2 (transmitting station) is provided with theconfiguration of the base station BS2 as shown in FIG. 9. The channelstate estimating section 206 in the mobile station MT2 estimates achannel state between the mobile station MT1 (receiving station) in theradio communication system 1 and the mobile station MT2 (transmittingstation) in the radio communication system 2. For example, the channelstate estimating section 206 in the mobile station MT2 estimates thechannel state based on a known symbol of an uplink transmission signalfrom the mobile station MT1. The transmission determining section 202 inthe mobile station MT2 determines whether transmission of the uplinksignal UL2 from the mobile station MT2 is possible or not based on thebroadcast load information and the estimated channel state.

According to the mobile station MT2 in the radio communication system 2according to Modification 2-3, when a frequency band is shared betweenthe downlink signal DL1 in the radio communication system 1 and theuplink signal UL2 in the radio communication system 2, it is determinedwhether transmission of the uplink signal UL2 from the mobile stationMT2 is possible or not based on the channel state between the mobilestation MT1 and mobile station MT2, in addition to the load informationcollected in the base station BS1. Therefore, when the base station BS1that transmits the downlink signal DL1 exists near the mobile stationMT2, it is possible to prevent the quality of the downlink signal DL1transmitted from the base station BS1 from deteriorating due tointerference from the uplink signal UL2 transmitted from the mobilestation MT2.

Embodiment 3

Referring to FIG. 11, described next are the base station BS1 in theradio communication system 1 and the base station BS2 in the radiocommunication system 2 according to Embodiment 3 of the invention, whilefocusing on differences from those in Embodiment 1.

In the following, Embodiment 3 describes the case where a frequency bandis shared between the uplink signal UL1 in the radio communicationsystem 1 and the downlink signal DL2 in the radio communication system 2(see FIG. 5).

As shown in FIG. 11, the base station BS1 in the radio communicationsystem 1 has a QoS information collecting section 105 and resourceallocation control section 106, and in this respect, differs from thatin Embodiment 1.

The QoS information collecting section 105 in the base station BS1collects priority information in the radio communication system 1.Herein, the priority information is a priority of a signal indicated bythe QoS information. In Embodiment 3, since a shared frequency band isused in the uplink signal UL1, the QoS information collecting section105 collects the priority information of the uplink signal UL1.

The resource allocation control section 106 (frequency band switchingsection) in the base station BS1 performs resource allocation control ofthe uplink signal UL1 based on at least one of the priority informationof the downlink signal DL2 from the base station BS2, priorityinformation of the uplink signal UL1 collected in the QoS informationcollecting section 105 and reception quality information of the uplinksignal UL1 collected in the load information collecting section 102.

Herein, the resource allocation control is to switch a frequency bandused in transmission of signals between a dedicated frequency band ofthe radio communication system 1 and a shared frequency band, as shownin FIG. 12. For example, in FIG. 12, the shared frequency band is usedas frequency bands of mobile stations MT11 and MT22 hard to receiveinterference between the radio communication systems 1 and 2 (see FIG.1), and the dedicated frequency band of the radio communication system 1is used as frequency bands of mobile stations MT12 and MT21 apt toreceive interference between the radio communication systems 1 and 2.

More specifically, when the reception quality of the uplink signal UL1falls below a predetermined value, the resource allocation controlsection 106 switches the frequency band of the uplink signal UL1 fromthe shared frequency band to the dedicated frequency band of the radiocommunication system 1.

Further, when the priority of the uplink signal UL1 is higher than thepriority of the downlink signal DL2, the resource allocation controlsection 106 may switch the frequency band of the uplink signal UL1 fromthe shared frequency band to the dedicated frequency band of the radiocommunication system 1.

The base station BS2 in the radio communication system 2 has a QoSinformation collecting section 207 and resource allocation controlsection 208, and in this respect, differs from that in Embodiment 1.

The QoS information collecting section 207 in the base station BS2collects the priority information in the radio communication system 2,and particularly, in Embodiment 3, collects the priority information ofthe downlink signal DL2.

The resource allocation control section 208 in the base station BS2performs resource allocation control of the downlink signal DL2 based onat least one of the priority information of the uplink signal UL1 fromthe base station BS1, priority information of the downlink signal DL2collected in the QoS information collecting section 207 and receptionquality information of the downlink signal DL2. In addition, theresource allocation control section 208 performs switching control ofthe frequency band on the downlink signal DL2 as described specificallyin the resource allocation control section 106 in the base station BS1.

The frequency band sharing processing according to Embodiment 3 will bedescribed below with reference to FIG. 13. In Embodiment 3, the sharedfrequency band is shared between the uplink signal UL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2, and the frequency band sharing processing isperformed between the base station BS1 (receiving station) in the radiocommunication system 1 and the base station BS2 (transmitting station)in the radio communication system 2.

As shown in FIG. 13, the load information collecting section 102 and QoSinformation collecting section 105 in the base station BS1 respectivelycollect the load information and priority information of the uplinksignal UL1 (step S301). Steps S302 to S306 are the same as steps S102 toS106 in FIG. 4, and descriptions thereof are omitted.

The broadcast signal transmitting/receiving section 201 in the basestation BS2 transmits a broadcast signal to the base station BS1. Thebroadcast signal includes the priority information of the downlinksignal DL2, in addition to the predicted interference power caused inthe base station BS1 due to transmission of the downlink signal DL2(step S307). The broadcast signal transmitting/receiving section 103 inthe base station BS1 receives the broadcast signal from the base stationBS2 (step S308).

The resource allocation control section 106 in the base station BS1determines whether or not to switch the frequency band of the uplinksignal UL1 from the shared frequency band to the dedicated frequencyband of the radio communication system 1, based on at least one of thepriority information of the downlink signal DL2 included in thebroadcast signal, the priority information of the uplink signal UL1collected in step S301, and the reception quality information of theuplink signal UL1. The resource allocation control section 106 instructsthe mobile station MT1 to switch the frequency band of the uplink signalUL1 based on the determination result (step S309). Steps S310 and S311are the same as steps S109 and S110 in FIG. 4, and descriptions thereofare omitted.

According to the base station BS1 in the radio communication system 1according to Embodiment 3, when a shared frequency band is sharedbetween the uplink signal UL1 in the radio communication system 1 andthe downlink signal DL2 in the radio communication system 2, withrespect to the uplink signal UL1 of which signal quality is not improvedeven by allowable interference level control in the shared frequencyband, the frequency band is switched from the shared frequency band tothe dedicated frequency band of the radio communication system 1.Therefore, even when interference increases from the downlink signal DL2transmitted using the shared frequency band, it is possible to improvethe quality of the uplink signal UL1 in the radio communication system 1

(Modification 3-1)

Modification 3-1 in Embodiment 3 describes the case where a frequencyband is shared between the uplink signal UL1 in the radio communicationsystem 1 and the uplink signal UL2 in the radio communication system 2(see FIG. 6), while focusing on the difference from Embodiment 3.

In the frequency band sharing processing according to Modification 3-1,the mobile station MT2 is provided with the configuration of the basestation BS2 as shown in FIG. 11. In Modification 3-1, the mobile stationMT2 (transmitting station) in the radio communication system 2 transmitsa broadcast signal including the predicted interference power caused inthe base station BS1 due to transmission of the uplink signal UL2 andthe priority information of the uplink signal UL2 to the base stationBS1 (receiving station) in the radio communication system 1. The basestation BS1 instructs the mobile station MT1 to switch the frequencyband of the uplink signal UL1 from the shared frequency band to thededicated frequency band of the radio communication system 1, based onat least one of the priority information of the uplink signal UL2included in the broadcast signal, the priority information of the uplinksignal UL1, and the reception quality information of the uplink signalUL1.

According to the base station BS1 in the radio communication system 1according to Modification 3-1, with respect to the uplink signal UL1 ofwhich signal quality is not improved even by allowable interferencelevel control in the shared frequency band, the frequency band isswitched from the shared frequency band to the dedicated frequency bandof the radio communication system 1. Therefore, even when interferenceincreases from the uplink signal UL2 transmitted using the sharedfrequency band, it is possible to improve the quality of the uplinksignal UL1 in the radio communication system 1.

(Modification 3-2)

Modification 3-2 in Embodiment 3 describes the case where a frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the downlink signal DL2 in the radiocommunication system 2 (see FIG. 7), while focusing on the differencefrom Embodiment 3.

In the frequency band sharing processing according to Modification 3-2,the base station BS1 (transmitting station) in the radio communicationsystem 1 collects the priority information of the downlink signal DL1,and switches the frequency band of the downlink signal DL1 from theshared frequency band to the dedicated frequency band of the radiocommunication system 1, based on at least one of the collected priorityinformation of the downlink signal DL1, the reception qualityinformation of the downlink signal DL1, and the priority information ofthe downlink signal DL2 broadcast from the base station BS2(transmitting station) in the radio communication system 2.

According to the base station BS1 in the radio communication system 1according to Modification 3-2, with respect to the downlink signal DL1of which signal quality is not improved even by allowable interferencelevel control in the shared frequency band, the frequency band isswitched from the shared frequency band to the dedicated frequency bandof the radio communication system 1. Therefore, even when interferenceincreases from the downlink signal DL2 transmitted using the sharedfrequency band, it is possible to improve the quality of the downlinksignal DL1 in the radio communication system 1.

(Modification 3-3)

Modification 3-3 in Embodiment 3 describes the case where a frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 in the radiocommunication system 2 (see FIG. 8). In the frequency band sharingprocessing according to Modification 3-3, the mobile station MT2 isprovided with the configuration of the base station BS2 as shown in FIG.11. The mobile station MT2 (transmitting station) performs the sameprocessing as in Modification 3-1. Further, the base station BS1(transmitting station) performs the same processing as in Modification3-2.

According to the base station BS1 in the radio communication system 1according to Modification 3-3, with respect to the downlink signal DL1of which signal quality is not improved even by allowable interferencelevel control in the shared frequency band, the frequency band isswitched to the dedicated frequency band of the radio communicationsystem 1. Therefore, even when interference increases from the uplinksignal UL2 transmitted using the shared frequency band, it is possibleto improve the quality of the downlink signal DL1 in the radiocommunication system 1.

Embodiment 4

Referring to FIG. 14, the base station BS2 in the radio communicationsystem 2 according to Embodiment 4 of the invention will be describedbelow, while focusing on differences from those in Embodiment 3 andModifications 3-1 to 3-3.

In Embodiment 4, when a shared frequency band is used in the downlinksignal DL2 in the radio communication system 2, the base station BS2(transmitting station) has a load information collecting section 209.When a shared frequency band is used in the uplink signal UL2, themobile station MT2 (transmitting station) has the load informationcollecting section 209.

The load information collecting section 209 collects the loadinformation of the radio communication system 2. More specifically, theload information collecting section 209 in the base station BS2 collectsthe load information of the downlink signal DL2, when the sharedfrequency band is used in the downlink signal DL2 in the radiocommunication system 2. Meanwhile, the load information collectingsection 209 in the mobile station MT2 collects the load information ofthe uplink signal UL2, when the shared frequency band is used in theuplink signal UL2 in the radio communication system 2.

The broadcast signal transmitting/receiving section 201 transmits, tothe base station BS1 in the radio communication system 1, a broadcastsignal including the load information of the radio communication system2 collected in the load information collecting section 209, in additionto the predicted interference power calculated in the predictedinterference power calculating section 204 and the priority informationcollected in the QoS information collecting section 207.

The resource allocation control section 106 in the base station BS1performs the resource allocation control of the uplink signal UL1 ordownlink signal DL1 using the shared frequency band, based on at leastone of the priority information of the downlink signal DL2 or uplinksignal UL2 broadcast from the base station BS2 or mobile station MT2,the load information of the radio communication system 2, and thepriority information of the uplink signal UL1 or downlink signal DL1collected in the QoS information collecting section 105.

For example, when the broadcast load on the radio communication system 2falls below a predetermined value, the resource allocation controlsection 106 switches the frequency band of the uplink signal UL1 ordownlink signal DL1 using the shared frequency band to the dedicatedfrequency band of the radio communication system 1.

According to the base station BS2 or mobile station MT2 in the radiocommunication system 2 according to Embodiment 4, the load informationof the radio communication system 2 is broadcast to the base station BS1in the radio communication system 1, and in accordance with the loadinformation of the radio communication system 2, the base station BS1switches the frequency band of the uplink signal UL1 or downlink signalDL1 using the shared frequency band to the dedicated frequency band ofthe radio communication system 1. Therefore, it is possible to reducethe interference to the radio communication system 2 by the uplinksignal UL1 or downlink signal DL1 transmitted using the shared frequencyband, and to improve the signal quality in the radio communicationsystem 2.

Embodiment 5

Referring to FIG. 15, described next is the base station BS1 in theradio communication system 1 according to Embodiment 5 of the invention.The base station BS1 according to Embodiment 5 is only applied to thecase that a share frequency band is used in the downlink signal DL1.Accordingly, Embodiment 5 describes the case that the shared frequencyband is shared between the downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 or downlink signal DL2in the radio communication system 2 (see FIG. 7 or 8).

As shown in FIG. 15, the base station BS1 (receiving station) in theradio communication system 1 has an adjacent cell interference controlsection 107. The adjacent cell interference control section 107 performsadjacent cell interference control of a cell C1 of the base station BS1based on the predicted interference power broadcast from the basestation BS2. The adjacent cell interference control is control to reducethe interference power caused in the mobile station MT1 in the cell C1by cells adjacent to cell C1 of the base station BS1. More specifically,the adjacent cell interference control section 107 instructs basestations in cells adjacent to the cell C1 to restrict the load on thedownlink signal.

The frequency band sharing processing according to Embodiment 5 will bedescribed below with reference to FIG. 16. In Embodiment 5, as describedabove, the frequency band of the downlink signal DL1 in the radiocommunication system 1 is the shared frequency band, and the frequencyband sharing processing is performed between the base station BS1(receiving station) in the radio communication system 1 and the basestation BS2 or mobile station MT2 (transmitting station) in the radiocommunication system 2. In addition, steps S401 to S408 are the same assteps S101 to S108 in FIG. 4, and descriptions thereof are omitted.

As described above, the adjacent cell interference control section 107in the base station BS1 instructs base stations in cells adjacent to thecell C1 to restrict the load on the downlink signal, based on thepredicted interference power broadcast from the base station BS2 ormobile station MT2 (step S409). Steps S410 and S411 are the same assteps S109 and S110 in FIG. 4, and descriptions thereof are omitted.

According to the base station BS1 in the radio communication system 1according to Embodiment 5, when the frequency band of the downlinksignal DL1 in the radio communication system 1 is the shared frequencyband, adjacent cell interference control is performed on base stationsin cells adjacent to the cell C1 of the base station BS1 based on thepredicted interference power broadcast from the base station BS2.Therefore, it is possible to prevent the signal quality of the downlinksignal DL1 from deteriorating due to interference from the adjacentcells, and to enhance the allowable interference level of the downlinksignal DL1 against interference from the radio communication system 2.

Embodiment 6

Referring to FIG. 17, the base station BS1 in the radio communicationsystem 1 according to Embodiment 6 of the invention will be describedbelow, while focusing on differences from those in Embodiment 1 andModifications 1-1 to 1-3.

Embodiment 6 collectively describes the case that a frequency band isshared between the uplink signal UL1 or downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 or downlink signal DL2in the radio communication system 2 (see FIGS. 5 to 8).

In Embodiment 6, when the frequency band of the downlink signal DL2 inthe radio communication system 2 is the shared frequency band (see FIGS.5 and 7), the base station BS1 in the radio communication system 1performs the determination whether transmission of the downlink signalDL2 is possible or not, although the determination is performed by thebase station BS2 in the radio communication system2 in above Embodiment.Further, in Embodiment 6, when the frequency band of the uplink signalUL2 in the radio communication system 2 is the shared frequency band(see FIGS. 6 and 8), the base station BS1 in the radio communicationsystem 1 performs the determination on whether or not transmission ofthe uplink signal UL2 is possible or not, although the determination isperformed by the mobile station MT2 in the radio communication system 2in above Embodiment.

As shown in FIG. 7, the base station BS1 in the radio communicationsystem 1 has an allowable interference level calculating section 108 andtransmission determining section 109.

The allowable interference level calculating section 108 calculates anallowable interference level margin in the radio communication system 1based on the load information of the radio communication system 1collected in the load information collecting section 102.

The transmission determining section 109 determines whether transmissionof the uplink signal UL2 or downlink signal DL2 using the sharedfrequency band is possible or not in the radio communication system 2,based on the predicted interference power broadcast from the basestation BS2.

More specifically, the transmission determining section 109 determinesthat it is possible to transmit the uplink signal UL2 or the downlinksignal DL2 using the shared frequency band, when the allowableinterference level margin calculated in the allowable interference levelcalculating section 108 is the predicted interference power broadcastfrom the base station BS2 or more. Meanwhile, the transmissiondetermining section 109 determines that it is impossible to transmit theuplink signal UL2 or the downlink signal DL2 using the shared frequencyband, when the allowable interference level margin calculated in theallowable interference level calculating section 108 is less than thepredicted interference power broadcast from the base station BS2.

Referring to FIG. 18, described next is the frequency band sharingprocessing according to Embodiment 6. In Embodiment 6, as describedabove, corresponding to whether the shared frequency band is thefrequency band of the downlink signal DL2 or uplink signal UL2 in theradio communication system 2, the frequency band sharing processing isperformed between the base station BS1 in the radio communication system1 and the base station BS2 or mobile station MT2 in the radiocommunication system 2.

The load information collecting section 102 in the base station BS1collects the load information of the uplink signal UL1 or downlinksignal DL1 using the shared frequency band (step S501)

The allowable interference level calculating section 108 in the basestation BS1 calculates an allowable interference level margin in theradio communication system 1, based on the load information of the radiocommunication system 1 collected in the load information collectingsection 102 (step S502)

In the base station BS2 or mobile station MT2, a transmission request ismade for the downlink signal DL2 or uplink signal UL2 (step S503).

The transmission parameter determining section 203 in the base stationBS2 or mobile station MT2 determines the transmission power of thedownlink signal DL2 or uplink signal UL2. The predicted interferencepower calculating section 204 calculates the predicted interferencepower caused in the base station BS1 or mobile station MT1 by thedownlink signal DL2 or uplink signal UL2 to be transmitted using theshared frequency band, based on the transmission power determined in thetransmission parameter determining section 203 (step S504).

The broadcast signal transmitting/receiving section 201 in the basestation BS2 or mobile station MT2 transmits a broadcast signal includingthe calculated predicted interference power to the base station BS1(step S505). The broadcast signal transmitting/receiving section 103 inthe base station BS1 receives the broadcast signal including thepredicted interference power (step S506).

The transmission determining section 109 in the base station BS1determines whether transmission of the downlink signal DL2 or uplinksignal UL2 using the shared frequency band is possible or not in theradio communication system 2. More specifically, it is determinedwhether or not the allowable interference level margin calculated instep S502 is the predicted interference power broadcast in step S506 ormore (step S507).

When it is determined that transmission of the downlink signal DL2 oruplink signal UL2 is possible, the broadcast signaltransmitting/receiving section 103 in the base station BS1 transmits abroadcast signal including transmission permission of the downlinksignal DL2 or uplink signal UL2 (step S508). The allowable interferencelevel control section 104 in the base station BS1 increases an allowableinterference level of the uplink signal UL1 or downlink signal DL1 (stepS509).

The broadcast signal transmitting/receiving section 201 in the basestation BS2 or mobile station MT2 receives the broadcast signalincluding transmission permission of the downlink signal DL2 or uplinksignal UL2 (step S510).

When the transmission permission of the downlink signal DL2 or uplinksignal UL2 is received, the signal transmitting/receiving section 205 inthe base station BS2 or mobile station MT2 transmits the downlink signalDL2 or uplink signal UL2 according to transmission parameters determinedin step S504 (step S511).

Meanwhile, when the transmission permission of the downlink signal DL2or uplink signal UL2 is not received, the base station BS2 or mobilestation MT2 waits for transmission of the downlink signal DL2 or uplinksignal UL2 (step S512).

According to the base station BS1 in the radio communication system 1according to Embodiment 6, instead of the base station BS2 or mobilestation MT2 in the radio communication system 2, the base station BS1determines whether transmission of the downlink signal DL2 or uplinksignal UL2 using the shared frequency band is possible or not.Therefore, it is possible to reduce the processing load on the basestation BS2 that transmits the downlink signal DL2 or the mobile stationMT2 that transmits the uplink signal UL2 using the shared frequency bandin the radio communication system 2.

Embodiment 7

Referring to FIG. 19, the base station BS2 in the radio communicationsystem 2 according to Embodiment 7 of the invention will be describedbelow, while focusing on differences from those in Embodiment 1 andModifications 1-1 to 1-3.

Embodiment 7 collectively describes the case that a frequency band isshared between the uplink signal UL1 or downlink signal DL1 in the radiocommunication system 1 and the uplink signal UL2 or downlink signal DL2in the radio communication system 2 (see FIGS. 5 to 8). As describedabove, when the frequency band of the downlink signal DL2 is the sharedfrequency band (see FIGS. 5 and 7), the above-mentioned configuration ofthe transmission determining section 202, etc is provided in the basestation BS1 (transmitting station), while being provided in the mobilestation MT2 when the frequency band of the uplink signal UL2 is theshared frequency band (see FIGS. 6 and 8).

As shown in FIG. 19, the transmission determining section 202 determineswhether or not the allowable interference level margin in the radiocommunication system 1 that is estimated based on the load informationfrom the base station BS1 is a predetermined value or more (step S604),as described in above-mentioned Embodiments 1 to 6.

In addition to the first determination whether the transmission ispossible or not in step S604, the transmission determining section 202makes a second determination whether the transmission is possible or notbased on comparison between the predicted interference power calculatedin the predicted interference power calculating section 204 and theallowable interference level margin in the radio communication system 1(step S607). More specifically, the transmission determining section 202determines that it is possible to transmit the downlink signal DL2 oruplink signal UL2, when the allowable interference level margin is thepredicted interference power or more, while determining that it is notpossible to transmit the downlink signal DL2 or the uplink signal UL2,when the allowable interference level margin is not more than thepredicted interference power.

According to the base station BS2 or mobile station MT2 in the radiocommunication system 2 according to Embodiment 7, as well as the firstdetermination whether transmission of the downlink signal DL2 or uplinksignal UL2 is possible or not, the base station BS2 or mobile stationMT2 makes the second determination whether the transmission is possibleor not based on comparison between the allowable interference levelmargin in the radio communication system 1 and the predictedinterference power. Therefore, even when the allowable interferencelevel margin in the radio communication system 1 has an allowance tosome extent, in the case where the predicted interference power from thedownlink DL2 or uplink UL2 to be transmitted using the shared frequencyband exceeds the allowable interference level margin (for example, inthe case where a receiver in the radio communication system 1 and atransmitter in the radio communication system 2 exist in mutually closepositions), it is possible to prevent the deterioration of the qualityof the uplink signal UL1 or downlink signal DL1 using the sharedfrequency band in the radio communication system 1.

Other Embodiments

In Embodiments 1 to 5 and corresponding Modifications, the transmissionparameter determining section 203 determines the transmission power ofthe downlink signal DL2 or uplink signal UL2 using the shared frequencyband, not based on the allowable interference level margin in the radiocommunication system 1, but may determine the transmission power not toexceed the allowable interference level margin in the radiocommunication system 1. According to such a method, it is possible touse the allowable interference level margin of the radio communicationsystem 1 to the limit such that the radio communication system 2 iscapable of using.

In Embodiment 3 and Modifications 3-1 to 3-3, it is described that theresource allocation control section 106 of the base station BS1 in theradio communication system 1 as shown in FIG. 11 performs the resourceallocation control of the uplink signal UL1 (or the downlink signal DL1)in the radio communication system 1, based on at least one of thepriority information of the downlink signal DL2 (or the uplink signalUL2) in the radio communication system 2, the priority information ofthe uplink signal UL1 (or downlink signal DL1) in the radiocommunication system 1, and the reception quality information of theuplink signal UL1 (or downlink signal DL1) in the radio communicationsystem 1. However, the resource allocation control section 106 mayperform the resource allocation control in the radio communicationsystem 1 based on ease of undergoing interference from the transmittingstation in the radio communication system 2, as a substitute for theabove-mentioned priority information.

For example, the resource allocation control section 106 may perform theresource allocation control in the radio communication system 1 based onan estimation result of the channel state between the receiving station(base station BS1 or mobile station MT1) receiving the signal using theshared frequency band in the radio communication system 1 and thetransmitting station (base station BS2 or mobile station MT2)transmitting the signal using the shared frequency band in the radiocommunication system 2. Similarly, the resource allocation controlsection 208 in the base station BS2 (or the mobile station MT2) in theradio communication system 2 as shown in FIG. 11 may perform theresource allocation control in the radio communication system 2 based onan estimation result of the channel state as described above. Inaddition, as described in Embodiment 2 and Modifications 2-1 to 2-3, theabove-mentioned channel state is capable of being estimated by thechannel state estimating section 206 as shown in FIG. 9.

In Embodiment 7, as shown in FIG. 19, the first determination (stepS604) and second determination (step S607) are made on whethertransmission of the downlink signal DL2 or uplink signal UL2 using theshared frequency band is possible or not, but only the seconddetermination may be made without making the first determination.

In the above-mentioned Embodiments and corresponding Modifications, itis described that the base station BS1 performs the allowableinterference level control in both of the case that the shared frequencyband is used on the uplink UL1 in the radio communication system 1 (seeFIGS. 5 and 6) and the case that the shared frequency band is used onthe downlink DL1 in the radio communication system 1 (see FIGS. 7 and8). However, the receiving station receiving the signal using the sharedfrequency band in the radio communication system 1 may perform theallowable interference level control. More specifically, it is possibleto adopt the configuration that the base station BS1 performs theallowable interference level control, as described above, when theshared frequency band is used on the uplink UL1 in the radiocommunication system 1, and that the mobile station MT1 performs theallowable interference level control when the shared frequency band isused on the downlink DL1 in the radio communication system 1.

When the shared frequency band is used on the downlink DL1 in the radiocommunication system 1 and the mobile station MT1 performs the allowableinterference level control, the mobile station MT1 is provided with theconfiguration of the base station BS1 as shown in FIG. 2. In this case,the load information collecting section 102 in the mobile station MT1collects the load information (for example, the traffic amount of thedownlink signal DL1, reception quality information of the downlinksignal DL1, etc.). The broadcast signal transmitting/receiving section103 in the mobile station MT1 broadcasts the signal to the transmittingstation (base station BS2 or mobile station MT2) that transmits thesignal using the shared frequency band in the radio communication system2. The allowable interference level control section 104 in the mobilestation MT1 increases the allowable interference level of the downlinksignal DL1 transmitted using the shared frequency band, based on thepredicted interference power broadcast from the transmitting station.More specifically, the mobile station MT2 instructs the base station BS1to increase the transmission power of the downlink signal DL1 ordecrease a transmission rate of the downlink signal DL1, based on thebroadcast predicted interference power.

Further, it is possible to combine configurations of Embodiments 1 to 5,Embodiment 7 and other Embodiments. Furthermore, the present inventionis not limited to the above-mentioned Embodiments, and is capable ofbeing carried into practice with various modifications thereof. Forexample, processing sections and processing procedures are capable ofbeing carried into practice with various modifications thereof asappropriate without departing from the scope of the invention. Moreover,the invention is capable of being carried into practice with variousmodifications thereof as appropriate without departing from the scope ofthe invention.

1. A radio station for controlling a first radio communication systemsignal transmitted using a shared frequency band which a first radiocommunication system uses in priority to a second radio communicationsystem, comprising: a broadcast section that broadcasts load informationof the first radio communication system to a transmitting station in thesecond radio communication system; an acquisition section that acquirespredicted interference power caused in a receiving station in the firstradio communication system by a second radio communication system signalthat is transmitted using the shared frequency band from thetransmitting station in the second radio communication system; and anallowable interference level control section that increases an allowableinterference level of the first radio communication system signaltransmitted using the shared frequency band, based on the predictedinterference power acquired in the acquisition section.
 2. The radiostation according to claim 1, wherein the allowable interference levelcontrol section increases transmission power of the first radiocommunication system signal or decreases a transmission rate of thefirst radio communication system signal, based on the predictedinterference power acquired in the acquisition section.
 3. The radiostation according to claim 1, further comprising: a frequency bandswitching section that switches a frequency band of the first radiocommunication system signal from the shared frequency band to adedicated frequency band of the first radio communication system,wherein the acquisition section acquires priority information of thefirst radio communication system signal and the second radiocommunication system signal, and reception quality information of thefirst radio communication system signal, in addition to the predictedinterference power, and the frequency band switching section switchesthe frequency band of the first radio communication system signal fromthe shared frequency band to the dedicated frequency band, based on atleast one of the priority information and the reception qualityinformation.
 4. The radio station according to claim 3, wherein theacquisition section acquires load information of the second radiocommunication system, in addition to the predicted interference power,the priority information and the reception quality information, and thefrequency band switching section switches the frequency band of thefirst radio communication system signal from the shared frequency bandto the dedicated frequency band, based on at least one of the priorityinformation, the reception quality information, and the load informationof the second radio communication system.
 5. The radio station accordingto claim 1, further comprising: an adjacent cell interference controlsection that decreases interference power caused in the receivingstation in the first radio communication system by an adjacent cell,based on the predicted interference power acquired in the acquisitionsection.
 6. A transmitting station for transmitting a second radiocommunication system signal to a receiving station in a second radiocommunication system, using a shared frequency band which a first radiocommunication system uses in priority to the second radio communicationsystem, comprising: an acquisition section that acquires loadinformation of the first radio communication system; a transmissiondetermining section that determines whether transmission of the secondradio communication system signal using the shared frequency band ispossible or not, based on the load information acquired in theacquisition section; a predicted interference power calculating sectionthat calculates predicted interference power caused in a receivingstation in the first radio communication system by the second radiocommunication system signal transmitted using the shared frequency band;and a broadcast section that broadcasts the predicted interference powercalculated in the predicted interference power calculating section tothe first radio communication system.
 7. The transmitting stationaccording to claim 6, further comprising: a channel state estimatingsection that estimates a channel state between the receiving station inthe first radio communication system and the transmitting station,wherein the transmission determining section determines whethertransmission of the second radio communication system signal using theshared frequency band is possible or not, based on the load informationacquired in the acquisition section and the channel state estimated inthe channel state estimating section.
 8. The transmitting stationaccording to claim 6, wherein the broadcast section broadcasts priorityinformation of the second radio communication system signal transmittedusing the shared frequency band, in addition to the predictedinterference power.
 9. The transmitting station according to claim 8,wherein the broadcast section broadcasts load information of the secondradio communication system, in addition to the predicted interferencepower and the priority information.
 10. A frequency band sharing methodin which a first radio communication system and a second radiocommunication system share a shared frequency band which the first radiocommunication system uses in priority to the second radio communicationsystem, comprising: broadcasting, in a radio station in the first radiocommunication system, load information of the first radio communicationsystem to a transmitting station in the second radio communicationsystem; determining, in the transmitting station in the second radiocommunication system, whether transmission of a second radiocommunication system signal from the transmitting station using theshared frequency band is possible or not, based on the broadcast loadinformation of the first radio communication system; calculating, in thetransmitting station in the second radio communication system, predictedinterference power caused in a receiving station in the first radiocommunication system by the second radio communication system signaltransmitted using the shared frequency band; broadcasting, in thetransmitting station in the second radio communication system, thecalculated predicted interference power to the radio station in thefirst radio communication system; and increasing, in the radio stationin the first radio communication system, an allowable interference levelof a first radio communication system signal transmitted using theshared frequency band, based on the broadcast predicted interferencepower.